Analysis of solidification parameters during solidification of lead and aluminum base alloys

Abstract

Experiments were carried out in which the conditions of columnar to equiaxed transition (CET) in directional solidification of dendritic alloys are known, in alloy systems such as Pb–Sn, Al–Cu, Al–Si, Al–Mg and Al–Zn. These experiments allow determining that the transition does not occur in an abrupt form in the samples and it is presented when the gradient in the liquid ahead of the columnar dendrites reaches critical and minimum values, being negative in most of the cases. The transition occurs when the temperature gradients in the melt ahead of the columnar dendrites are in the range of −0.80 to 1.0 °C/cm for Pb–Sn, −11.41 to 2.80 °C/cm for Al–Cu, −4.20 to 0.67 °C/cm for Al–Si, −1.67 to 0.91 °C/cm for Al–Mg, −11.38 to 0.91 °C/cm for Al–Zn. Two interfaces are defined, assumed to be macroscopically flat, the liquidus and solidus interfaces. When the CET occurs, the speed of the liquidus front accelerates much faster than the speed of the solidus front, the values were 0.004 to 0.01, 0.02 to 0.48, 0.12 to 0.89, 0.10 to 0.18 and 0.09 to 0.18 cm/s, respectively. Also, the average supercooling of 0.63 to 2.75 °C for Pb–Sn, 0.59 to 1.15 °C for Al–Cu, 0.67 to 1.25 °C for Al–Si, 0.69 to 1.15 °C for Al–Mg and 0.85 to 1.40 °C for the Al–Zn alloys were measured, which provides the driving force to surmount the energy barrier required to create a viable solid–liquid interface. The results obtained in all alloys systems are compared and analyzed.